Howto convert Step(*.stp) to AutoCAD(*.fbx) with python Script (and also decimate the face ratio)
Is there a way to import *.stp File in to blender, with out converting the *.stp file in to *.stl or other by Blender acceptable type with external tools?


Unfortunately no. The current import tools available in Blender do not allow (to my knowledge) to read and / or interpret NURBS input data. Some way or another, this always has to be processed by an external application first, and then be brought into Blender in a second step.

There are a few tools out there which can assist in this, you already mentioned FreeCAD which does a good job on less complicated input files. Many times however you're stuck with proprietary commercial software. A solution that works well is Autodesk Showcase. It reads many industry standard formats, allows for dynamic tessellation of parts / files, gives you a nice visual representation, and exports well to .fbx, which is the preferred format (for me) to bring stuff into Blender. Main advantage: With this pipeline, custom split normals are generated and imported correctly.


  After I've imported an object with 'bpy.ops.import_mesh.stl(filepath=stl_in)' do I get with 'bpy.context.object' to some thing like number_of_surfaces/polygons?


Of course. You can use len(bpy.context.object.data.polygons) to get the polycount of the active object. len(bpy.context.object.data.vertices) and len(bpy.context.object.data.edges) are the vertex and edge counterparts. In essence, bpy.context.object.data.polygons and the like are Python lists, where you can access each individual face / edge / vertex.